docs: def implementation_optimize_tck(tck):
      '''Converts 1-d or 2-d splines calculated with SciPy's `splrep` or
      `bisplrep` to a format for fastest computation - lists in PyPy, and numpy
      arrays otherwise.
      
      Only implemented for 3 and 5 length `tck`s.
      '''
      if IS_PYPY:
          return tck
      else:
          if len(tck) == 3:
              tck[0] = np.array(tck[0])
              tck[1] = np.array(tck[1])
          elif len(tck) == 5:
              tck[0] = np.array(tck[0])
              tck[1] = np.array(tck[1])
              tck[2] = np.array(tck[2])
          else:
              raise NotImplementedError
      return tck